The primary goal of this grant is to understand the early events of chemosensory transduction in mammalian taste receptor cells. Using a combination of patch-clamp and optical recording techniques on isolated hamster taste cells and loose-patch recording from hamster taste cells in situ, the following hypothesis will be tested: Taste stimuli interact with apically-located ion channels or receptors, resulting in membrane depolarization, action potential initiation and Ca++ influx. Particular cell types respond selectively to taste stimuli. Specifically, the following questions will be addressed: 1. What are the mechanisms used by hamster taste cells to transduce salty, sour, sweet and bitter taste stimuli into receptor potentials? A. Salt/sour: What are the single channel properties of the amiloride- sensitive Na+ channel? What is the mechanism of the amiloride- insensitive Na+ response? What is the role of the amiloride-sensitive Na+ channel in sour (acid) transduction? Do any other mechanisms participate in the transduction of sour stimuli? (collaboration with S. Roper) B. Sweet: What are the respective roles of cAMP and cGMP in sweet taste transduction? What are the ion channel targets of these nucleotides? Is phosphorylation involved? C. Bitter: What is the relative importance of phosphoinositide turnover, phosphodiesterase activation, and K+ channel block in bitter taste transduction? 2. What is the role of the action potential in taste transduction? What stimuli elicit action potentials in taste cells, and does electrical activity reflect changes in intracellular Ca++? Are action potentials required for triggering an increase in intracellular Ca++ in response to taste stimuli? 3. Are taste cells narrowly or broadly tuned to taste stimuli? Do taste cells of a particular type respond selectively to taste stimuli? (collaboration with J. Kinnamon) These studies will provide important new information about mechanisms of taste transduction, the role of the action potential and Ca++ in transmitter release, and the cellular basis of taste discrimination.